Catheters as tubular medical instruments serve for investigating or treating hollow organs in the body. Ablation catheters are a special kind of catheter which are equipped with an electrode and which, using high-frequency electromagnetic waves, permit targeted denaturing of tissue in the heart. Electrophysiological therapy of that kind is usually applied for treating cardiac disrhythmia. In order to position the electrode which is mounted in the region in the tip of the catheter in the heart appropriately for the function involved through the primary vein or artery, the catheter is provided with a control or adjusting mechanism, by means of which the region of the tip of the catheter can be deflected from the exterior in a plurality of directions, that is to say it can be pivoted. The catheter can be targetedly positioned manually by appropriate pivotal movement of the tip of the catheter in conjunction with a forward displacement of the guide tube.
A catheter of the general kind set forth is known from U.S. Pat. No. 5,273,535 to Edwards. The catheter essentially comprises a gripping or handle element which goes into a catheter stem from which extends a flexible guide tube which terminates in a catheter tip with integrated electrode. Disposed at the end of the gripping element which is opposite to the catheter stem is an electric line, by way of which the electrode is supplied with electrical energy.
Two draw wires which are secured to the tip of the catheter extend within the flexible guide tube. The draw wires are arranged in such a way that pulling on one draw wire or the other makes it possible to deflect the tip of the catheter in a first direction or in a direction opposite to the first direction. The draw wires do not provide for the transmission of a pressure force. By virtue of deflection of the tip of the catheter and an additional rotary movement of the guide tube by means of the gripping element, the catheter can follow the curved configuration of a hollow organ in the body, without causing damage thereto.
The draw wires are movable alternately in a pulling mode by way of transmission means which are disposed in the gripping element and which are operated manually by a control element. The control element is here in the form of a control wheel. The transmission means convert the rotary movement of the control wheel into the pulling longitudinal movement for the draw wires. The transmission means comprise a shaft which is arranged stationarily and coaxially with respect to the control wheel and against which a respective draw wire bears from each of both sides. The two draw wires are secured to an apex point on the shaft. If now for example a rotary movement in the counterclockwise direction is effected at the control wheel, then the shaft also rotates in the counterclockwise direction and a wire is wound on to the shaft corresponding to the angle of rotation covered, and is thereby pulled. The other draw wire is correspondingly relieved of load. This involves a deflection movement of the tip of the catheter. Deflection in the opposite direction is produced in a similar manner by way of rotation of the control wheel in the clockwise direction. With this structure, the degree of deflection is established by the diameter of the shaft and is really slight by virtue of the structural boundary conditions involved.
The transmission means further include a locking mechanism in the form of a locking screw in order if necessary to hold the deflected catheter tip in position, that is to say, to prevent it from springing back into the straight position.
Other transmission means are known from U.S. Pat. No. 5,254,088, to Lundquist. Thus, a wedge element which is displaceable in orthogonal relationship to the gripping element can be provided as the control element. Displacement of the wedge element causes pulling of a draw wire which is connected to the wedge element by way of a longitudinal groove. A second draw wire can be operated in the same manner by way of a further wedge element. Handling of these control elements however is really complicated and the degree of deflection in that case is severely limited. As a second alternative, proposed as the control element is a rocker-like pivotal lever which is mounted at the center pivotably in the gripping element and which at both sides of the mounting location has two clamping locations for gripping the draw wires. The pivotal lever which projects on both sides beyond the gripping element makes handling of the catheter more difficult and the degree of deflection is also limited by the angle of pivotal movement. Admittedly, an increase in the distance of the wire-clamping locations from the mounting location could increase the degree of deflection in this arrangement; that however also involves the draw wires spreading to a greater degree, so that handling is worsened due to frictional influences. A third proposed alternative makes use of two control wheels which are arranged one behind the other, with associated shafts, on which a respective draw wire can be wound separately to any desired length. That structure admittedly permits a high degree of deflection but handling is really complicated by the two control wheels to be operated.
U.S. Pat. No. 5,364,351 to Heinzelman discloses a catheter whose transmission means include two racks. A draw wire is disposed at the end of each rack. The racks are arranged to face towards each other with their teeth and are guided longitudinally movably within the gripping element. Engaging therebetween is a gear which is connected to a manual control wheel by way of further gears. This structure can permit a high degree of deflection of the tip of the catheter, by alternate rotary movement at the control wheel. The transmission means however comprise a large number of movable individual parts which each have to be supported or guided according to their respective function.
Therefore the object of the present invention is to provide a catheter, in particular an ablation catheter, which is simple in structure and which is in addition precise in terms of handling.
Based on a catheter as set forth in the classifying portion of claim 1, that object is attained in conjunction with the characterising features thereof. Advantageous developments of the invention are set forth in the following appendant claims.
The invention includes the technical teaching that provided as a transmission means for a catheter is a toothed drive pulley which is coupled to a manual control wheel and which correspondingly comes into engagement in the teeth of a toothed belt which is guided by way of guide means within the gripping element in such a way that at least one draw wire is pullingly longitudinally movable by way of an entrainment member secured to one flank side of the toothed belt. Precisely two draw wires can be arranged at both flank sides of the toothed belt for bidirectional deflection.
The structure according to the invention has the advantage that a high degree of deflection of the tip of the catheter is possible as the degree of deflection is dependent on the length of the flank side, that is to say ultimately the periphery of the toothed belt used. The structural size of the gripping element can in that way be kept relatively small, which is to the advantage of manual operability. Furthermore the structure according to the invention manages with a small number of individual parts, thereby simplifying the structural configuration involved. Precise handling is governed by the configuration of the draw wires, which is effected very substantially straight and centrally in the gripping element, due to the arrangement of the entrainment members. Due to the resulting, only slight degree of spread relative to the point of entry into the flexible guide tube on the catheter stem, movement of the draw wires can take place with a minimum amount of friction, which guarantees easily movable operation. Only a small amount of control force is required at the control wheel, with the drive pulley-pulling means combination according to the invention.
The guide means can be in the form of a toothed guide pulley which is arranged opposite the toothed drive pulley, the two pulleys jointly with the toothed belt forming a pulling means transmission. It is also possible for the guide means to be in the form of an U-shaped or L-shaped rail which is arranged opposite the toothed drive pulley. Preferably the U-shaped rail can be formed directly by the internal configuration of the gripping element. That situation involves the elimination of separate components for the drive means.
Preferably the entrainment member comprises a fixing portion which correspondingly co-operates in positively locking relationship with the teeth of the toothed belt and which is thus non-displaceable, and an eye portion for a crimp sleeve secured at the end to the draw wire, to permit a pulling movement of the draw wire. The eye portion-crimp sleeve arrangement means that the draw wire can be pulled and prevents the disadvantageous application of a pressure force to the draw wire.
A further feature which improves the invention provides that arranged on the control wheel are friction brake means in order to prevent unwanted resilient return movement of the deflected tip of the catheter. The friction brake means apply a constant frictional force over the entire control movement of the control wheel and thus permit jerk-free fine displacement.
Another improving feature provides that manually variable adjusting means are provided for setting the spacing and the angular position between the gripping portion and a catheter stem. That permits simple adjustment of draw wires, deflection planes and corrugational configuring of the stem.